U.S. patent application number 11/031204 was filed with the patent office on 2006-07-06 for method and system for displaying an image.
This patent application is currently assigned to Texas Instruments Incorporated. Invention is credited to Jeffrey Matthew Kempf, Daniel J. Morgan.
Application Number | 20060145975 11/031204 |
Document ID | / |
Family ID | 36639795 |
Filed Date | 2006-07-06 |
United States Patent
Application |
20060145975 |
Kind Code |
A1 |
Kempf; Jeffrey Matthew ; et
al. |
July 6, 2006 |
Method and system for displaying an image
Abstract
A method for displaying an image using a digital micromirror
device having a plurality of mirrors operable to assume a plurality
of positions is provided. The method includes receiving a plurality
of numbers representing a respective plurality of pixels that form
a plurality of dither patterns. Each dither pattern is a particular
portion of the image to be displayed and each pixel is represented
by a particular number. The method also includes assigning, to each
number, an address identifying a particular one of the plurality of
mirrors in a particular position. The address is unique among the
addresses assigned to each of the plurality of numbers. The method
also includes displaying the dither patterns one after another in a
predetermined frame time period using the digital micromirror
device. The dither patterns are displayed by showing each pixel on
a display according to the number representing the pixel. Each
pixel is shown using the particular mirror in the particular
position identified by the address that is assigned to the
number.
Inventors: |
Kempf; Jeffrey Matthew;
(Dallas, TX) ; Morgan; Daniel J.; (Denton,
TX) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
US
|
Assignee: |
Texas Instruments
Incorporated
|
Family ID: |
36639795 |
Appl. No.: |
11/031204 |
Filed: |
January 6, 2005 |
Current U.S.
Class: |
345/84 |
Current CPC
Class: |
G09G 2340/0464 20130101;
G09G 2320/0276 20130101; G09G 3/2055 20130101; G09G 3/2051
20130101; G09G 3/007 20130101; G09G 3/346 20130101 |
Class at
Publication: |
345/084 |
International
Class: |
G09G 3/34 20060101
G09G003/34 |
Claims
1. A method for displaying an image, comprising: providing a
digital micromirror device having a plurality of micromirrors
operable to oscillate between a plurality of positions; receiving a
plurality of binary numbers each indicating a light intensity level
for a particular one of a plurality of pixels that form a plurality
of dither patterns, wherein each dither pattern is a particular
portion of the image to be displayed; assigning, to each binary
number, an address that is unique among the addresses assigned to
each of the plurality of binary numbers, wherein the address
identifies a particular one of the plurality of micromirrors in a
particular position; and displaying the dither patterns one after
another in a predetermined frame time period using the digital
micromirror device by showing each pixel on a display according to
the binary number representing the pixel, the each pixel shown
using the particular one of the micromirrors in the particular
position identified by the address assigned to the binary
number.
2. The method of claim 1, wherein each dither pattern is configured
so that the image, when shown by displaying the dither patterns one
after another in the frame time period, comprises a high frequency
noise.
3. The method of claim 1, wherein the plurality of positions
comprises only two positions, and the plurality of dither patterns
comprises only two dither patterns.
4. The method of claim 1, wherein the plurality of positions
comprises only four positions and the plurality of dither patterns
comprises only four dither patterns.
5. A method for displaying an image using a digital micromirror
device having a plurality of mirrors operable to assume a plurality
of positions, the method comprising: receiving a plurality of
numbers representing a respective plurality of pixels that form a
plurality of dither patterns, wherein each dither pattern is a
particular portion of the image to be displayed and each pixel is
represented by a particular number; assigning, to each number, an
address identifying a particular one of the plurality of mirrors in
a particular position, the address being unique among the addresses
assigned to each of the plurality of numbers; and displaying the
dither patterns one after another in a predetermined frame time
period using the digital micromirror device by showing each pixel
on a display according to the number representing the pixel, the
each pixel shown using the particular mirror in the particular
position identified by the address assigned to the number.
6. The method of claim 5, wherein each dither pattern is configured
so that the image, when shown by displaying the dither patterns one
after another in the frame time period, comprises a high frequency
noise.
7. The method of claim 5, wherein each dither pattern comprises a
high frequency noise.
8. The method of claim 5, wherein the plurality of dither patterns
comprises only two dither patterns.
9. The method of claim 5, wherein the plurality of dither patterns
comprises only four dither patterns.
10. The method of claim 5, wherein the plurality of numbers
comprises a plurality of binary numbers representing a particular
level of light intensity.
11. The method of claim 5, and further comprising: receiving an
image feed representing the image in analog format; and converting
the image feed into the plurality of numbers.
12. The method of claim 5, and further comprising: receiving an
image feed representing the image in a format that is used for
displaying the image using a cathode ray tube; applying a de-gamma
correction to the image feed; and converting the corrected image
feed into the plurality of numbers.
13. The method of claim 5, wherein the address corresponds to a
unique location on the image.
14. A system for displaying an image using a digital micromirror
device having a plurality of mirrors operable to assume a plurality
of positions, the system comprising: a processor; a computer
readable medium accessible to the processor and storing a program
operable, when executed by the processor, to: receive a plurality
of numbers representing a respective plurality of pixels that form
a plurality of dither patterns, wherein each dither pattern is a
particular portion of the image to be displayed and each pixel is
represented by a particular number; assign, to each number, an
address identifying a particular one of the plurality of mirrors in
a particular position, the address being unique among the addresses
assigned to each of the plurality of numbers; and display the
dither patterns one after another in a predetermined frame time
period using the digital micromirror device by showing each pixel
on a display according to the number representing the pixel, the
each pixel shown using the particular mirror in the particular
position identified by the address assigned to the number.
15. The system of claim 14, wherein each dither pattern is
configured so that the image, when shown by displaying the dither
patterns one after another in the frame time period, comprises a
high frequency noise.
16. The system of claim 14, wherein each dither pattern comprises a
high frequency noise.
17. The system of claim 14, wherein the plurality of dither
patterns comprises only two dither patterns.
18. The system of claim 14, wherein the plurality of dither
patterns comprises only four dither patterns.
19. The system of claim 14, wherein the plurality of numbers
comprises a plurality of binary numbers each representing a
particular level of light intensity.
20. The system of claim 14, and further comprising a decoder
coupled with the processor, the decoder operable to: receive an
image feed representing the image in analog format; and convert the
image feed into the plurality of numbers.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] This invention relates generally to visual displays and more
particularly to a method and system for displaying an image.
BACKGROUND OF THE INVENTION
[0002] Television displays and other types of displays often
receive a data stream that is decoded by a decoder. Often, such
decoders possess inadequate resolution for high resolution
displays. For example, eight bit decoders may be utilized where
twelve or fourteen bit decoders would be more desirable.
[0003] This problem of inadequate bit resolution is exacerbated by
other processing steps used in digital light processing systems.
For example, to account for the non-linear response of a cathode
ray tube, television signal images traditionally have a non-linear
transfer function applied, and the non-linear response is provided
as the input signal. This non-linear function is referred to as a
gamma correction curve. However, in linear devices such as Digital
Light Processing (DLP) Systems available from Texas Instruments, a
de-gamma function may need to be applied to the incoming pixel
stream to correct the unneeded gamma correction.
[0004] Because of the non-linear nature of the gamma and the
de-gamma curves, linear devices such as the DLP system may require
a finer grayscale resolution of approximately 14-16 bits at the low
end of the grayscale curve. However, some optical semiconductors
that are used in DLP systems, such as the Digital Micromirror
Device (DMD.TM.) available from Texas instruments, may have a
grayscale resolution limit of 8-10 bits. To bridge the gap in
resolution, mechanical and electronic dithering may be used to
achieve the perception of 14-16 bit grayscale resolution.
Mechanical and electronic dithering may result in images that have
clumped portions and/or frequency noises that are undesirable for
certain types of images, which lower the perceived quality of the
image.
SUMMARY OF THE INVENTION
[0005] According to one embodiment, a method for displaying an
image using a digital micromirror device having a plurality of
mirrors operable to assume a plurality of positions is provided.
The method includes receiving a plurality of numbers representing a
respective plurality of pixels that form a plurality of dither
patterns. Each dither pattern is a particular portion of the image
to be displayed and each pixel is represented by a particular
number. The method also includes assigning, to each number, an
address identifying a particular one of the plurality of mirrors in
a particular position. The address is unique among the addresses
assigned to each of the plurality of numbers. The method also
includes displaying the dither patterns one after another in a
predetermined frame time period using the digital micromirror
device. The dither patterns are displayed by showing each pixel on
a display according to the number representing the pixel. Each
pixel is shown using the particular mirror in the particular
position identified by the address that is assigned to the
number.
[0006] Some embodiments of the invention provide numerous technical
advantages. Some embodiments may benefit from some, none, or all of
these advantages. For example, in one embodiment of the invention,
the noise characteristic of an image displayed in a frame period
can be controlled by synchronizing the mechanical and electronic
dithering. In another embodiment, clumping may be reduced.
[0007] Other advantages are readily apparent to those of skill in
the art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] For a more complete understanding of embodiments of the
invention, reference is now made to the following description,
taken in conjunction with the accompanying drawings, in which:
[0009] FIG. 1 is a block diagram showing portions of a light
processing system according to the teachings of the invention;
[0010] FIG. 2 is a schematic diagram illustrating example address
values for pixels that form an image to be displayed in a frame
time;
[0011] FIG. 3A is a schematic diagram illustrating example address
values for pixels that form a first subframe of the image to be
displayed in a frame time;
[0012] FIG. 3B is a schematic diagram illustrating example address
values for pixels that form a second subframe of the image to be
displayed in a frame time; and
[0013] FIG. 4 is a flowchart illustrating one embodiment of a
method for synchronizing electrical and mechanical dithering.
DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION
[0014] Example embodiments of the invention and its advantages are
best understood by referring to FIGS. 1 through 4 of the drawings,
like numerals being used for like and corresponding parts of the
various drawings.
[0015] FIG. 1 is a block diagram of a light processing system 10
according to the teachings of the present invention. One example of
system 10 is a DLP system, which is a liner display system. System
10 receives a data source 12, such as a television feed. Source 12
may be received by a decoder 14, which decodes the analog source
signal and generates a plurality of digital bits. Conventionally, a
plurality of bits are utilized to represent a value corresponding
to an intensity level for a particular pixel to be displayed. This
value is referred to as pixel data, an example of which is a binary
number. The plurality of digital bits (binary numbers, for example)
are sent from decoder 14 to a de-gamma block 15. De-gamma block 15
is operable to apply a de-gamma function to correct the television
data that is conditioned to account for the non-linear response of
a CRT image. Stated in other words, de-gamma block 15 is used to
transform the data source from a non-linear space to a linear
space, because a linear display system, such as a DLP system, does
not use a CRT image. Image data processed by de-gamma block 15 is
sent to a dither pattern generator 18, which operates to divide the
image data into data representing multiple dither patterns. The
dither patterns are to be shown one after another in a rapid
succession within a predetermined frame time period, and a viewer
perceives the successive showing of dither patterns as one complete
image frame. Because a dither pattern is shown as one of the
subframes of a frame, a dither pattern is also referred to as a
subframe-level image or a subframe. The complete image shown by
displaying the subframes within a frame time is referred to as a
frame-level image, or a "super-resolution" image.
[0016] Referring again to FIG. 1, the dither patterns from
generator 18 are provided to a formatter 20, which operates to
assign pixel addresses to pixel data of each dither pattern. The
address correlates the pixel data with a particular device, such as
a particular mirror of a DMD.TM., that will be used to show the
pixel according to the pixel data. Conventionally, the addressing
scheme used to assign addresses is at a subframe level, which means
that the same set of address values is used for each of the
subframes. Thus, a first subframe and a second subframe may each
have pixel data that has the same address. The data representing
each dither pattern is sent to memories 24 and 28 to be stored.
This data is then provided to a microcontroller 24 for displaying
the subframes within a frame time period using a display 28.
[0017] Because of the non-linear nature of the gamma and the
de-gamma curves, linear devices such as the DLP system may require
finer resolution of approximately 14-16 bits of grayscale
resolution at the lower end of the grayscale. However, some optical
semiconductors such as DMD.TM., which uses a rectangular array of
microscopic mirrors to modulate light, may have a grayscale
resolution limit of 8-10 bits due to certain mechanical limitations
associated with the speed in which mirrors can be tilted. To bridge
the gap in resolution, mechanical and electronic dithering may be
used to achieve the perception of 14-16 bit grayscale
resolution.
[0018] Mechanical dithering refers to a technique where the
micromirrors of a DMD.TM. are oscillated between multiple positions
within a single frame time to achieve an increase in perceived
resolution without increasing the array size. Because each discrete
position allows the mirrors to be used for showing a different set
of pixels, the rapid oscillation between positions increases the
perceived resolution of an image by a multiple of the number of
positions. For example, a rectilinear display may oscillate between
four discrete positions for a quadruple increase in perceived
resolution, and a diamond display may oscillate between two
discrete positions to double the perceived resolution. Each
position assumed by the mirrors during a particular frame time
period may be used to display a subframe of an image.
[0019] Electronic dithering, such as Blue-Noise Spatial-Temporal
Multiplexing (BN STM), refers to a technique where an image is
divided into multiple portions each having a blue-noise dither
pattern (also referred to as high frequency noise dither pattern).
The multiple portions are shown in rapid succession within a frame
time to show a complete image. Because one dither pattern is shown
at a time and the patterns are shown in rapid succession, the
perceived resolution of an image may be increased without
increasing the actual array size. An image resulting from using
both mechanical and electronic dithering may have unintended
clumped portions, a high frequency noise, or a low frequency noise,
which, depending on the situation, may lower the perceived quality
of the image.
[0020] According to one embodiment of the invention, a system and
method are provided that improve the quality of image shown using a
DMD.TM. by synchronizing the electronic dithering with mechanical
dithering, which allows control over the noise characteristic of an
image shown in a frame time. In one embodiment, this is
advantageous because the image perceived by a viewer is more
pleasing to the viewer. In another embodiment, clumping is
controlled, which improves the quality of the perceived image.
Additional details of example embodiments of the invention are
described in greater detail below in conjunction with portions of
FIG. 1 and FIGS. 2 through 4.
[0021] Referring again to FIG. 1, formatter 20 includes a program
22 operable to assign pixel addresses to pixel data of dither
patterns using an addressing scheme for a frame-level image rather
than one for a sub-frame level image. For example, each binary
number that represents each one of the pixels forming the dither
patterns may be assigned an address from a set of address values
for a frame-level image. Because an addressing scheme for a
frame-level image is used to uniquely identify each pixel at a
frame level, each binary number for each pixel of all dither
patterns for a frame is assigned an address value that is unique
among the assigned addresses of other binary numbers for other
dither patterns of the frame. For example, in an embodiment where
two dither patterns are to be shown in a single frame time, no
binary number representing a particular pixel in the first dither
pattern would be assigned the same address value as another binary
number representing another pixel of the first or second dither
patterns. An example of address values used in a frame-level
addressing scheme is described below in conjunction with FIG. 2. By
using a frame-level addressing scheme, each of dither patterns
generated as a part of electronic dithering may be synchronized
with a particular position of a mechanical dithering. This allows
control over what dither pattern is shown as which subframe, which
in turn allows each dither pattern to be designed to avoid clumping
and undesirable noises in a resulting frame-level image. Referring
again to FIG. 1, the addressed data is sent to memories 24 and 28
to be stored. The data is then provided to microcontroller 24 for
controlling display on display 28.
[0022] FIG. 2 is a schematic diagram showing an example a plurality
of pixels 50 each associated with an address value under a
frame-level addressing scheme. In some embodiments, pixels 50
represent a frame-level image that may be shown using a portion of
display 34 shown in FIG. 1. As shown in FIG. 2, in some
embodiments, pixels 50 comprise thirty pixels 50 arranged in a
five-by-six block. A plurality of blocks of pixels, such as the
block of pixels 50 shown in FIG. 2, may be arranged so that the
respective frame-level images formed by the blocks of pixels 50
together form a complete picture on display 34. In other words,
pixels 50 shown in FIG. 2 represent a piece of a mosaic. Although
pixels 50 are shown as a five-by-six block, any suitable
configuration may be used to arrange any number of pixels 50.
[0023] Referring again to FIG. 2, each pixel 50 is associated with
a frame-level address value, and program 22 of FIG. 1 may assign
frame-level address values, such as the ones shown in FIG. 2, to
each binary number representing associated each pixel of each
dither pattern. Although examples of frame-level address values are
shown as numbers from "0" to "29," any suitable identifiers that
can be used to distinguish one pixel address from other pixel
addresses may be used.
[0024] Pixels 50 are arranged in rows, such as rows 56 and 60, and
columns, such as columns 62 and 64. For example, as shown in FIG.
2, address values are addressed in raster scan order, with pixels
50 in row 58 addressed "0" to "4" from left to right, pixels 50 in
row 60 addressed "5" to "9" from left to right, and so forth.
However, in some embodiments, pixels 50 may be addressed in any
suitable manner, and may be arranged in any suitable configuration
that may be different than the example configuration shown in FIG.
2.
[0025] FIG. 3A shows pixels 80 that form a first dither pattern,
and FIG. 3B shows pixels 100 that form a second dither pattern.
FIGS. 3A and 3B are described jointly. In an example where a
two-position, diamond mechanical dithering is used, pixels 80 shown
in FIG. 3A may correspond to position one, and pixels 100 shown in
FIG. 3B may correspond to position two. Position one is where the
mirrors of a DMD.TM. are tilted downward by half of a pixel and
position two is where the mirrors are tilted upward by half of a
pixel. Each position assumed in mechanical dithering is used to
show a subframe of an image, as described above. A dither pattern
shown in a particular subframe constitutes a portion of the
frame-level image. Thus, when all subframes are successively shown
through the oscillation of mirrors between the two positions in a
frame time, the viewer perceives the combined showing of the
subframes as a frame-level image. According to some embodiments,
pixels 80 for position one and pixels 100 for position two are
addressed using two mutually exclusive groups of address values
shown in FIG. 2, respectively. Thus, no pixel 80 shares the same
address value as a pixel 100, and each address corresponds to a
particular mirror that is assuming a particular position. For
example, an address value shown as "1" in FIGS. 2 and 3A may
correspond to a particular mirror of a DMD.TM. that is in a
downward tilt position, and an address value shown as "6" in FIGS.
2 and 3B may correspond to the same mirror that is assuming an
upward tilt position. In one embodiment, pixels 80 and 100 are
respectively associated with odd and even address values shown in
FIG. 2, which is one way of ensuring the assignment of unique
address values. Because unique addresses are associated with for
each one of pixels 80 and 100, pixel data for each pixel of the
image to be displayed is uniquely addressed within an image space,
such as the image space represented by pixel spaces 50 in FIG. 2.
Because data for each pixel of a dither pattern is addressed using
these unique addresses, as shown in FIGS. 3A and 3B, a dither
pattern can be generated for each subframe to control the noise
characteristics of each dither pattern and to reduce the clumping
that may result from showing multiple subframes.
[0026] FIG. 4 is a flowchart illustrating one embodiment of a
method 150 for displaying an image. Method 150 is described using
pixels 50, 80, and 100 shown in FIGS. 2, 3A, and 3B, respectively.
However, any pixels and any suitable frame-level addressing scheme
may be used. Program 22 shown in FIG. 1 is used as an example
implementation of some portions of method 150. However, any
suitable software or hardware implementation method may be used.
Method 150 may be used with any electronic and mechanical dithering
techniques, including the two-way and four-way optical
movements.
[0027] Method 150 starts at step 154. At step 158, image data of an
image to be displayed using display 34 is received at decoder 14
shown in FIG. 1. The image data may be processed suitably at
decoder 14, and the processed image may undergo gamma correction at
device 15. At step 160, the processed and corrected image data is
divided into data representing multiple dither patterns at
generator 18 shown in FIG. 1. Each dither pattern is to be
displayed as one of the subframes that will be displayed by display
34 within a frame period. In some embodiments, the image data is
divided into data representing multiple dither patterns so that
each dither pattern includes a high frequency noise or a low
frequency noise. In some embodiments, each dither pattern for the
image to be displayed may be patterned so that the image resulting
from the combined viewing of the subframes has a high frequency
noise or a low frequency noise regardless of whether an individual
dither pattern exhibits a high or low frequency noise. Thus,
depending on the particular noise characteristic that is desired
for a particular type of image (bright, dark, fast motion, or
standstill image, for example), it is possible to control the noise
characteristic of each of the subframes and/or other
characteristics of the frame-level image.
[0028] At step 164, program 22 assigns an address value to pixel
data, such as a binary number, for each pixel of each dither
pattern using a frame-level address scheme, an example of which is
shown in FIG. 2. Using frame-level address values allows each
dither pattern to be patterned so that the resulting outcome of
showing all of the subframes within a frame period can be
controlled to have either a high frequency noise characteristic or
a low frequency noise characteristic. At step 168, each dither
pattern is displayed as a subframe using the assigned addresses of
step 164. Method 150 stops at step 170.
[0029] Although some embodiments of the present invention have been
described in detail, it should be understood that various changes,
substitutions, and alterations can be made hereto without departing
from the spirit and scope of the invention as defined by the
appended claims.
* * * * *